Inspection method and inspection apparatus

ABSTRACT

Disclosed is an inspection method for inspecting the electrical characteristics of a device by bringing an inspecting probe into electrical contact with an inspection electrode. An insulating film formed on the surface of the inspection electrode is broken by utilizing a fritting phenomenon so as to bring the inspection electrode into electrical contact with the inspection electrode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2000-249702, filed Aug. 21,2000; and No. 2001-093303, filed Mar. 28, 2001, the entire contents ofboth of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an inspection method and an inspectionapparatus, particularly, to an inspection method and an inspectionapparatus which permit suppressing the needle pressure applied by aprobe to the inspection electrode of a target object to be inspected.

2. Description of the Related Art

In the manufacturing process of semiconductor devices, these devices areformed on a semiconductor wafer. Then, inspected are the electricalcharacteristics of the target object(s) to be inspected (hereinafterreferred to as “the device”) such as a device in the state of thesemiconductor wafer and a device cut away from the semiconductor waferand packaged. In the inspection process, the device is inspected bytransmitting and receiving an electric signal to and from a tester via aprobe electrically in contact with the inspection electrodes of thedevice.

Where the inspection electrode is formed of a material that is likely tobe oxidized such as aluminum, copper or a solder, an insulating filmsuch as an oxide film is formed on the surface of the inspectionelectrode in the inspecting stage. Therefore, even if the probe isbrought into contact with the inspection electrode, the electricalconnection between the two is not stabilized. Particularly, where theinspection electrode is made of aluminum, a very hard oxide film isformed on the surface of the inspection electrode, with the result thatit is very difficult to bring the probe into electrical contact with theinspection electrode.

In the prior art, the probe is brought into electrical contact with theinspection electrode by the mode shown in FIGS. 22A and 22B inaccordance with the flow chart shown in FIG. 21. Specifically, thepreparation for the inspection of the device is performed first (stepS1), followed by bringing the probe N into contact with the inspectionelectrode P with a predetermined pressure, e.g., 10 to 20 g/a probe, asshown in FIG. 22A (step S2). Then, it is judged whether or not the probeN has been brought into electrical contact with the inspection electrodeP (step S3). Where it is judged that electrical contact has beenachieved, the inspection is started (step S4). In general, it is judgedin step S3 that the probe N is not in electrical contact with theinspection electrode P by simply bringing the probe N into contact withthe inspection electrode P because an insulating film O is interposedbetween the two. In order to overcome the difficulty, the probe N andthe inspection electrode P are reciprocated relative to each other(scrubbed) as denoted by an arrow in FIG. 22B so as to scrape off theinsulating film O (step S5). In this step S5, the probe N is broughtinto electrical contact with the inspection electrode P. Afterelectrical contact has been confirmed, the inspection is started in stepS4.

Another method of breaking the insulating film O is to sharpen the tipof the probe. In this method, it is possible to increase the planarpressure given by the probe to the inspection electrode, making itpossible to permit the probe to be stuck into the inspection electrodeso as to ensure a good electrical contact between the two. In this case,it is necessary to stick the tip of the probe into the inspectionelectrode by at least 2,000 to 4,000 Å in order to ensure electricalcontact.

Recently, proposed is a probe card having fine probes each having adiameter of scores of microns formed in a silicon substrate with a smallpitch by using, for example, micro machine processing technology. Sincethe probe card has a micro structure, it is possible for the probe cardto cope with a high speed signal. In addition, since the probe is formedon a silicon substrate, the probe card is advantageous in that iteliminates the effects caused by the difference in the thermal expansioncoefficients of the probe card and the device in the heating test.

BRIEF SUMMARY OF THE INVENTION

In the method of scraping off the insulating film, it is possible forthe scraped dust of the insulating film to attach to the probe N, whichimpairs conduction. Therefore, it is not guaranteed that electricalcontact between the probe and the inspection electrode can be ensured bythe method described above. Further, the life of the probe N isshortened by the scrubbing and the yield of the manufactured device islowered because the inspection electrode P is scratched as shown in FIG.22B. It should be noted that the contact point between the probe N andthe inspection electrode P set in advance at the optimum position isaltered by the scrubbing. It has also been found that the device iscontaminated with the scraped dust scattered from the insulating film O,as shown in FIG. 22B. Such being the situation, it is necessary toperiodically remove the scraped dust of the insulating film from theprobe N, leading to a reduction in the inspection efficiency.

In the method in which the tip of the probe is stuck into the inspectionelectrode, the damage done to the inspection electrode is small.However, the inspection electrode is scratched as in the methoddescribed above. Also required is the durability for maintaining theshape of the tip portion of the probe. Since the degree of integrationof the devices has been markedly enhanced in recent years, theminiaturization of the device and the thinning of the film have beendrastically progressed. Under the circumstances, the thickness of theinspection electrode has been decreased such that, if the probe is stuckuntil the probe is brought into electrical contact with the inspectionelectrode, the underlying layer of the inspection electrode also tendsto be damaged.

The probe card manufactured by utilizing the micro machine processingtechnology has a fine probe structure, with the result that it isdifficult to apply a high needle pressure to the probe.

The present invention has been achieved in an attempt to overcome atleast one of the above-noted problems inherent in the prior art.

An object of an aspect of the present invention is to provide aninspection method and an inspection apparatus, which permit markedlydecreasing the needle pressure applied by the probe to the measuringelectrode.

Another object of an aspect of the present invention is to provide aninspection method and an inspection apparatus, which permit suppressingthe damage done to the inspection electrode and which also prolong thelife of the probe when used repeatedly.

Still another object of an aspect of the present invention is to providean inspection method and an inspection apparatus which reduce thenecessity of applying a cleaning treatment to the probe so as to improvethe inspecting efficiency.

Additional objects and advantages of an aspect of the present inventionwill be set forth in the description which follows, and in part will beobvious from the description, or may be learned by practice of thepresent invention. The objects and advantages of the present inventionmay be realized and obtained by means of the instrumentalities andcombinations particularly pointed out hereinafter.

According to a first aspect of the present invention, there is provideda method of inspecting a target object to be inspected, comprising thesteps of:

bringing about a fritting phenomenon in a part of the insulating filmformed on the inspection electrode of the target object to be inspectedso as to break a part of the insulating film;

bringing an inspecting probe into electrical contact with the surface ofa part of the inspection electrode, the insulating film of the part ofthe inspection electrode having been broken by the fritting phenomenon;and

inspecting the electrical characteristics of the target object by usinga tester connected to the inspecting probe.

It is desirable for the step of breaking a part of the insulating filmincluded in the inspection method described above to comprise the stepsof:

bringing a probe into contact with the inspection electrode of thetarget object to be inspected; and

applying a voltage between the probe and the inspection electrode so asto bring about the fritting phenomenon in the insulating film formed onthe surface of the inspection electrode.

It is also desirable for the step of breaking a part of the insulatingfilm comprises the steps of:

bringing a first probe and a second probe into contact with theinspection electrode of the target object; and

applying a voltage between the first probe and the second probe so as tobring about the fritting phenomenon in the insulating film formed on thesurface of the inspection electrode.

It is desirable for the inspection method described above to furthercomprise the step of inspecting the electrical characteristics of thetarget object to be inspected by utilizing, as the inspection electrode,at least one of the first probe and the second probe in contact with thesurface of a part of the inspection electrode, the insulating film ofthe part having been broken by the fritting phenomenon which has beenbrought about within the insulating film.

In the inspection method of the present invention, it is desirable forthe step of inspecting the electrical characteristics of the targetobject to be inspected by utilizing at least one of the first probe andthe second probe as the inspecting probe to comprise the step ofelectrically disconnecting the probe not utilized as the inspectingprobe, from at least one of the tester and the inspection electrode.

In the inspection method of the present invention, it is desirable forthe step of electrically disconnecting the probe from the inspectionelectrode to comprise the step of electrically separating the probe notutilized as an inspecting probe from the inspection electrode.

In the inspection method of the present invention, it is desirable forthe separating step to be performed by utilizing at least one of a piezoelement, a bimetal, and an electrostatic element.

According to a second aspect of the present invention, there is providedan inspection apparatus of a target object to be inspected, comprising:

a power source circuit for applying a voltage to a part of theinsulating film formed on the inspection electrode of the target objectso as to form a predetermined potential gradient in at least a part ofthe insulating film, a fritting phenomenon being formed in theinsulating film by the predetermined potential gradient so as to break apart of the insulating film;

an inspecting probe that is brought into electrical contact with thesurface of a part of the inspection electrode, the insulating film ofthe part of the inspection electrode having been broken by the frittingphenomenon; and

a tester connected to the inspecting probe so as to inspect theelectrical characteristics of the target object to be inspected.

It is desirable for the inspection apparatus to further comprise acurrent limiter for limiting the current flowing between the probe andthe inspection electrode.

In the inspection apparatus of the present invention, it is desirablefor the current limiter to form a predetermined potential gradient in atleast a part of the insulating film to comprise:

a first probe and a second probe each brought into contact with theinspection electrode of the target object to be inspected; and

a power source circuit for applying a voltage between the first probeand the second probe, the voltage serving to bring about a frittingphenomenon in the insulating film formed on the surface of theinspection electrode.

In the inspection apparatus of the present invention, it is desirablefor at least one of the first probe and the second probe to be formed ofat least one material selected from the group consisting of tungsten,palladium and a beryllium-copper alloy.

It is desirable for the inspection apparatus of the present invention tofurther comprise a controller for controlling the power source circuit,and a communication circuit for connecting the control means to thetester.

In the inspection apparatus of the present invention, it is desirablefor the means for forming a predetermined potential gradient in at leasta part of the insulating film to be incorporated in the tester.

In the inspection apparatus of the present invention, it is desirablefor the current limiter for limiting the current flowing between theprobe and the inspection electrode to be incorporated in the tester.

In the inspection apparatus of the present invention, it is desirablefor the power source circuit for forming a predetermined potentialgradient in at least a part of the insulating film to comprise:

a first probe and a second probe, which are brought into contact withthe inspection electrode of the target object to be inspected; and

a power source circuit for applying a voltage between the first probeand the second probe, the voltage serving to bring about a frittingphenomenon in the insulating film formed on the surface of theinspection electrode.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently embodiments of theinvention, and together with the general description given above and thedetailed description of the embodiments given below, serve to explainthe principles of the invention.

FIG. 1 shows the principle of a fritting apparatus used in theinspection method of an embodiment of the present invention;

FIG. 2 shows the construction of an inspection apparatus according toone embodiment of the present invention, to which is applied theprinciple shown in FIG. 1;

FIG. 3 is a flow chart showing an inspection method according to oneembodiment of the present invention;

FIGS. 4A-4B shows how the inspecting probe is brought into electricalcontact with the inspection electrode by the fritting phenomenon byusing the inspection apparatus shown in FIG. 2, wherein FIG. 4A showsthe state that an inspecting probe and a fritting probe are brought intocontact with an inspection electrode and a voltage is applied betweenthe inspecting probe and the fritting probe, and FIG. 4B shows the statethat the inspecting probe is brought into electrical contact with theinspection electrode by the fritting phenomenon;

FIG. 5 shows the construction of an inspection apparatus according toanother embodiment of the present invention;

FIG. 6 shows the construction of a measuring apparatus for verifying thefritting phenomenon;

FIG. 7 is a graph showing the waveforms of the current and the voltageexhibiting a typical fritting phenomenon;

FIG. 8 is a graph showing the waveforms of the current and the voltagewhen the insulating film is mechanically broken;

FIG. 9 is a graph showing the waveforms of the current and the voltagewhen the current in the fritting stage has not yet reached a limitvalue;

FIG. 10 is a graph showing the relationship between the needle pressureof the w (tungsten) probe and the fritting voltage;

FIG. 11 is a graph showing the relationship between the needle pressureof a BeCu probe and the fritting voltage;

FIG. 12 is a graph showing the relationship between the needle pressureof a Pd probe and the fritting voltage;

FIG. 13 is a graph showing the relationship between the maximum currentof the W (tungsten) probe and the contact resistance;

FIG. 14 is a graph showing the relationship between the maximum currentof a BeCu probe and the contact resistance;

FIG. 15 is a graph showing the relationship between the maximum currentof a Pd probe and the contact resistance;

FIG. 16 is a graph showing the relationship between the fritting voltageof each of the W probe, the BeCu probe and the Pd probe and the current;

FIG. 17 is a graph showing the relationship between the fritting voltageof each of the w probe, the BeCu probe and the Pd probe and the maximumcurrent;

FIG. 18 is a graph showing the relationship between the contactresistance between the W probe and the electrode after the fritting andseparating force;

FIG. 19 is a graph showing the relationship between the contactresistance between the BeCu probe and the electrode after the frittingand the separating force;

FIG. 20 is a graph showing the relationship between the contactresistance between the Pd probe and the electrode after the fritting andthe separating force;

FIG. 21 is a flow chart showing the conventional inspection method; and

FIGS. 22A-22B shows how the probe is brought into electrical contactwith the inspection electrode by the conventional inspection method,wherein FIG. 22A shows the state that the probe is brought into contactwith the inspection electrode, and FIG. 22B shows the state that theprobe is brought into electrical contact with the inspection electrodeby scrubbing.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 5 collectively show a first embodiment of the presentinvention. In the inspection method of the embodiment, a part of theinsulating film such as an oxide film formed on the surface of theinspection electrode of the device is broken by utilizing a frittingphenomenon. In the embodiment, the probe is brought into electricalcontact with the inspection electrode in the portion where theinsulating film is broken. It is possible to lower the needle pressurebetween the probe and the inspection electrode to a level lower than thepresent level of the needle pressure, i.e., the needle pressure can belowered to, for example, 0.1 g or less, by utilizing the frittingphenomenon. As a result, the inspection electrode is not scratched so asto prolong the life of the probe. The fritting phenomenon denotes thephenomenon that, if a voltage is applied to the insulating film such asan oxide film formed on the surface of a metal, i.e., the inspectionelectrode in the embodiment, in a manner to form a potential gradient ofabout 105 to 106 V/cm, the insulating film is subjected to insulationbreakdown because of the nonuniformity in the thickness of theinsulating film or in the composition of the metal so as to form acurrent path.

FIG. 1 shows the principle of a devised fritting apparatus used in theembodiment for bringing about a fritting phenomenon. As shown in FIG. 1,the fritting apparatus comprises a power source (ex. a programmablevoltage source) 1, a voltage-applied buffer amplifier 2, a resistor 3and an applied current limiter 4. The programmable voltage source 1applies voltage to a first probe 5A and a second probe 5B of a probecard 5. The first probe 5A is connected to the voltage-applied bufferamplifier 2 via the resistor 3, and the second probe 5B is connected tothe input terminal of the voltage-applied buffer amplifier 2 and to theground. It is desirable for each of these first and second probes 5A and5B to be made of a conductive metal such as tungsten (W), aberyllium-copper alloy (BeCu) or palladium (Pd).

The fritting apparatus of the construction described above is operatedas follows. Specifically, the first and second probes 5A and 5B of theprobe card 5 are brought into contact with the inspection electrode P ofa device D with a low needle pressure, e.g., 0.1 g or less. Under thiscondition, a voltage is applied from the programmable voltage source 1to the first probe 5A through the voltage-applied buffer amplifier 2 andthe resistor 3. Where the insulating film O is very thin, a slighttunnel current flows in the initial stage. The potential gradientbetween the first and second probes 5A and 5B is gradually increased bygradually increasing the voltage from the programmable voltage source 1so as to reach a predetermined potential gradient of about 105 to 106V/cm. As a result, the insulating film O positioned below the firstprobe 5A and the second probe 5B is broken so as to bring the firstprobe 5A and the second probe 5B into contact with the metal surface ofthe inspection electrode so as to rapidly increase the current flowingbetween the first probe 5A and the second probe 5B. The applied currentlimiter 4 detects the current so as to cause the voltage-applied bufferamplifier 2 to cease to apply voltage such that a further current doesnot flow. As a result, the first and second probes 5A and 5B are broughtinto electrical contact with the inspection electrode P so as to make itpossible to inspect the electrical characteristics of the device D.

FIG. 2 shows the construction of an inspection apparatus 10 according tothe first embodiment of the present invention, in which is employed theprinciple of the fritting apparatus shown in FIG. 1. The inspectionapparatus 10 according to the first embodiment of the present inventioncomprises a fritting apparatus 11 and a probe card 12, as shown in FIG.2. The inspection apparatus 10 is connected so as to communicate with atester 13 with power source 13A. On the other hand, the flittingapparatus 11 comprises a flitting circuit 14 serving to realize thefritting phenomenon and a flitting control circuit 15 serving to controlthe fritting circuit 14. The flitting control circuit 15 is connected tothe tester 13 through a general purpose communication circuit 16 such asan RS or a GPIB. The probe card 12 is provided with a pair of first andsecond probes 12A and 12B, which are collectively brought into contactwith an inspection electrode P arranged on the target object to beinspected. It is possible for the number of pairs of the first andsecond probes 12A, 12B to be equal to the number of inspectionelectrodes P of the target objects (devices) to be inspected. If anumber n of inspection electrodes P are formed on a single device, it ispossible to mount a number n of pairs of the first and second probes 12Aand 12B on the probe card 12. The second probe 12B is used only when theinsulating film O is broken by the fritting phenomenon. Therefore, inthe following description, the first probe 12A is called an inspectingprobe 12A and the second probe 12B is called a fritting probe 12B.

The power source circuit 13B may be considered as including the powersource 13A, the flitting circuit 14, and the flitting control circuit15, all of which can supply power a pair of first and second probes 12Aand 12B.

The fritting circuit 14 comprises a number n of circuits each consistingof an applied voltage buffer amplifier 14A, a resistor 14B, a currentdetection amplifier 14C, a current limiting amplifier 14D, and relayswitches 14E and 14F. The number n corresponds to the number of pairs ofthe inspecting probe 12A and the fritting probe 12B. The frittingcontrol circuit 15 serves to relay-control the relay switches 14E and14F. The relay switch 14E serves to switch the inspecting probe 12Abetween a contact 14G connected to the fritting apparatus 11 and acontact 14H connected to the tester 13. On the other hand, the relayswitch 14F performs the switching function between a ground potentialpoint 14I and a floating contact 14J. The inspecting probe 12A isconnected to the relay switch 14E, and the fritting probe 12B isconnected to the relay switch 14F. The high frequency characteristicscan be improved by connecting the relay switch 14F of the fritting probe12B to a point as close to the probe as possible. After the insulatingfilm O has been broken by the fritting phenomenon, it is desirable forthe fritting probe 12B to be disconnected from the tester. To achievethis particular state, it is possible to employ a mechanism fordisconnecting the wiring or a mechanism 18 for moving upward thefritting probe 12B so as to move the fritting probe 12B away from theinspection electrode. The mechanism 18 for moving the fritting probe 12Baway from the inspection electrode may be formed of, for example, apiezo element, a bimetal or an electrostatic element.

The inspection method according to an embodiment of the presentinvention, which is performed by using the inspection apparatus 10described above, will now be described with reference to FIGS. 3, 4A and4B. In the first step, the positions of the inspecting probe 12A and thefritting probe 12B are aligned with the position of the inspectionelectrode P of the device D (step S11). These probes 12A and 12B arebrought into contact with each inspection electrode P of the device Dwith a low needle pressure, e.g., 0.1 g or less, as shown in FIG. 4A(step S12). In this step, the relay switch 14E is switched to contact14G via the fritting control circuit 15, with the result that theinspecting probe 12A is connected to the fritting apparatus 11. Then,the relay switch 14F is switched to the ground contact 14I so as to begrounded. In this fashion, the probe card 12 is connected to thefritting apparatus 11.

The fritting operation is started by the voltage application from thefritting control circuit 15 to the inspecting probe 12A through theapplied voltage buffer amplifier 14A and the resistor 14B (step S13).Where the insulating film O is very thin, a tunnel current flows in thedirection denoted by an arrow in FIG. 4A in the initial stage of thevoltage application. The tunnel current is a very small current, farsmaller than the limiting current value. It is possible to determine thelimiting current value by the resistance value of the probes 12A and 12Bin contact with the inspection electrode, as shown in FIG. 4B. Thelimiting current valve is determined when the resistance valve is lowerthan 1 Ω, or preferably, lower than 0.5 Ω in the case where the probes12A and 12B are in contact with the inspection electrode, as shown inFIG. 4B. The very small current is detected by the current detectingamplifier 14C via the resistor 14B. The detected value is supplied tothe current limiting amplifier 14D. A limiting current is supplied as areference current from the fritting control circuit 15 to the currentlimiting amplifier 14D. The current limiting amplifier 14D compares thedetected current value generated from the current detection amplifier14C with the limiting current value (reference current value) generatedfrom the fritting limiting circuit 15 so as to judge whether or not thedetected current value has reached the limiting current (step S14).While the applied voltage from the fritting control circuit 15 isgradually elevated, the current limiting amplifier 14D judges whether ornot the current of the current sense resistor 14B has reached thelimiting current.

The electric potential gradient between the inspecting probe 12A and thefritting probe 12B is gradually increased by gradually increasing theapplied voltage from the voltage buffer amplifier 14A. If the electricpotential gradient is increased to a level at which the frittingphenomenon is brought about, the insulating film O on the surface of theinspection electrode P is broken by the fritting phenomenon as shown inFIG. 4B. When the detected current of the current detecting amplifier14C is rapidly increased to reach the limiting current, the voltageapplication from the applied voltage buffer amplifier 14A through thecurrent limiting amplifier 14D is stopped by the fritting phenomenon. Atthis stage, the inspecting probe 12A and the fritting probe 12B arebrought into electrical contact with the inspection electrode P so as toform the state under which the inspection can be performed. Under thisstate, the relay switch 14E is successively switched from the contact14G connected to the fritting apparatus 11 to the contact 14H connectedto the tester 13 under the control performed by the fritting controlcircuit 15. Also, the relay switch 14F is successively switched from theground contact 14I to the floating contact 14J in synchronism with theswitching of the relay switch 14E. As a result, the inspecting probe 12Ais connected to the tester 13 so as to cause the fritting probe 12B tofloat electrically. Under this state, the fritting control circuit 15notifies the tester 13 through the general purpose communication circuit16 that the state under which the inspection can be performed has beenformed. The tester 13 supplies an inspecting signal to the inspectingprobe 12A so as to inspect the electrical characteristics of the targetobject to be inspected (stage S15).

As described above, according to the first embodiment of the presentinvention, the insulating film O of the inspection electrode P is brokenunder the state that the inspecting probe 12A is brought into contactwith the inspection electrode P with a low needle pressure. As a result,the inspecting probe 12A is brought into electrical contact with theinspection electrode P so as to make it possible to perform theinspection of the electrical characteristics of the target object to beinspected without fail. Since the inspecting probe 12A is brought intoelectrical contact with the inspection electrode P with a very lowneedle pressure of 0.1 g, it is possible to improve the yield of thetarget object to be inspected without damaging the inspection electrodeP so as to prolong the life of the inspecting probe 12A. Since theinspection can be performed with the needle pressure of the inspectingprobe 12A set at 0.1 g or less, the inspection can be performed withoutfail even if the probe construction is simple such that the probe isformed by, for example, erecting a bonding wire. According to the firstembodiment of the present invention, the peeling dust is not generatedfrom the inspection electrode P, with the result that the target objectto be inspected is not contaminated with the peeling dust of theinspection electrode, and the peeling dust is not attached to theinspecting probe 12A. As a result, the yield is further improved. Inaddition, it is unnecessary to apply a cleaning treatment to theinspecting probe 12A so as to increase the inspecting efficiency.

According to the first embodiment of the present invention, the needlepressure applied to the inspecting probe 12A is low so as to increasethe degree of freedom in the construction of the needle tip and thebeam. Also, it is possible to ensure a large amount of overdrivingmovement of the inspecting probe 12A from the contact starting position.It is also possible to decrease the length of the beam for obtaining thesame needle pressure so as to make it possible to arrange the probes ina high density. Further, since the stability of the contact is unlikelyto be affected by the shape of the needle tip of the inspecting probe12A, it is unnecessary to process the needle tip in a special shape suchas a pyramidal shape.

Where the driver of the tester can be used as the flitting power source,it may suffice to mount a circuit for the relay 24F for connecting theflitting probe 12B to the ground as shown in FIG. 5. In other words, theinspecting probe 22A may be connected to the voltage power source (notshown) of the tester 23. The flitting probe 22B may be connected to therelay switch 24F. It is possible to use the I/O driver within the tester23 for the control of the relay switch 24F. Whether or not the flittingcan be performed by using the tester 23 depends on the power sourcecurrent capacity of the tester 23. In terms of the software, it maysuffice to add a program for the fritting to the program of the tester23. Also, in terms of the hardware, it may suffice to add a relaycircuit. Alternatively, it is possible for the tester itself to beprovided with a fritting power source, the fritting circuit 14 and thefritting control circuit 15. These embodiments also produce the functionand the effect similar to those produced by the embodiment shown in FIG.2.

The relationship between the material used for forming the probe and thefritting characteristics has been verified by using a measuringapparatus shown in FIG. 6. The results of the verification are shown inFIGS. 7 to 18.

FIG. 6 shows the construction of the measuring apparatus used in thisembodiment. The load (needle pressure) between a probe 51 and a wafer 50was measured by an electronic balance 52. The current and the voltageapplied by a power source 53 were measured by using an ammeter 54 and avoltage indicator 55. For measuring the waveform of the fritting, an A/Dconverters 56 and 57 was utilized. The current and the power sourcevoltage were measured and recorded. For the control of the probe 51 inthe Z-direction, a piezo stage 58 having a maximum displacement of 100μm was used. The piezo stage 58 was operated via a piezo driver 59. Allof the electronic balance 52, the power source 53, the ammeter 54, thevoltage indicator 55, the A/D converters 56, 57 and the piezo stage 58were connected to a computer 60 via a communication circuit (GPIB,RS-232C). The control of the applied voltage and the stage position wasperformed via the computer 60, and the results of the measurement wererecorded one by one. A loop of the voltage control, the voltagemeasurement, and the current measurement was performed repeatedly. Arate of the loop was about 10 times/sec. The measurement under highfrequency was performed by using the A/D converters 56 and 57 so as tomeasure the power source current flowing through the A/D converters 56and 57, respectively, and the power source voltage. The converted valuesfrom the A/D converters 56 and 57 were corrected by obtaining therelationship between the these converted values and the measured valuesof the ammeter 54 and the voltage indicator 55 and by using the measuredvalues of the ammeter 54 and the voltage indicator 55.

The measurement was performed under the measuring conditions given belowin accordance with the procedures (1) to (6) given below:

(1) The probe 51 was allowed to approach the wafer w by driving thepiezo stage 58. The needle pressure in this stage was monitored via theelectronic balance 52. The piezo stage 58 was stopped when the needlepressure exceeded a set needle pressure. The needle pressure in thisstage was determined as the contact load.

(2) A voltage was applied stepwise from the power source 53 so as togenerate a current and voltage. Immediately before application of thevoltage, the A/D converters 56 and 57 were started and the convertedvalues were recorded. The situation before and after application of thestepwise voltage was recorded in the memory of the A/D converters 56 and57.

(3) If a current not lower than 1 mA was recognized after the voltageapplication, it was considered that fritting had taken place. If thecurrent was not recognized, the applied voltage was returned to zero,and the measurement given in item (2) above was performed again with thevoltage set twice as high as before.

(4) After the occurrence of the fritting phenomenon, the voltage wasmeasured by setting the current at 1 mA. The resistance value calculatedfrom the measured voltage was determined as the contact resistance.

(5) After the applied voltage was returned to zero volts, the probe 51was moved away from the measuring electrode by driving the piezo stage58. It was considered that the minimum value of the load measured atthis stage was the separating force.

(6) The measurements of items (1) to (5) given above were repeated bychanging the contact position.

[Measuring Conditions]

(a) Voltage Control Mode (S)

Set voltage: 30 V, 5 V

Setting of current limiter: 10 mA, 100 mA, 250 mA

Needle pressure: 0.1 g, 0.02 g, 0.005 g, 0.001 g

(b) Current Control Mode (1)

Set current: 10 mA, 100 mA, 250 mA

Needle pressure: 0.1 g, 0.02 g, 0.005 g, 0.001 g

(c) Probe Material:

Tungsten (W), beryllium-copper alloy (BeCu), palladium (Pd)

(d) Electrode: aluminum (Al)

1. Waveform at Fritting Time

Changes with time in the voltage and current were measured by using atungsten probe, covering the cases where the needle pressure, thelimiting current and the set voltage were changed in various fashions.The waveforms of the voltage and the current before and after thefritting were measured so as to obtain waveforms of three typicalpatterns as shown in FIGS. 7 to 9.

The current and the voltage were measured by using the A/D converters 56and 57 under the condition that the current was controlled by settingthe limiting current at 10 mA by using a tungsten probe under a needlepressure of 0.01 g. FIG. 7 is a graph showing the waveforms of thecurrent denoted by a solid line and the voltage denoted by the brokenline at the time when the fritting took place. The graph shows thetypical waveform in the event of the fritting phenomenon. As shown inthe graph of FIG. 7, the fritting phenomenon takes place when thevoltage has reached a fritting voltage at which an insulation breakdownis brought about so as to cause the current to flow and the resistanceto be lowered. Although the maximum value of current is set at 10 mA bythe current limiter, it is seen that a large current flows for aninstant, because it takes time before the current limiter is operated.To be more specific, it is seen that a voltage of 6 V is applied at thetime when the current begins to flow so as to cause the current to flowin an amount exceeding 170 mA, and that the current limiter operatessubstantially simultaneously with the starting of the current flow so asto lower the voltage and the current to 10 mA, which is the set value ofthe limiting current.

The current and the voltage were measured by using the A/D converters 56and 57 under the condition that the current was controlled by settingthe limiting current at 250 mA and the voltage at 5 V by using atungsten probe under a needle pressure of 0.1 g. FIG. 8 is a graphshowing the waveforms of the current, which is denoted by a solid line,and the voltage, which is denoted by a broken line, at the time when thecurrent began to flow. As shown in the graph, the voltage and thecurrent change proportionally, in the case where the insulating film isbroken mechanically, not electrically. The current and the voltage weremeasured by using the A/D converters 56 and 57 under the condition thatthe current was controlled by setting the limiting current at 250 mA andthe voltage at 30 V by using a tungsten probe under a needle pressure of0.02 g. FIG. 9 is a graph showing the waveforms of the current, which isdenoted by a solid line, and the voltage, which is denoted by a brokenline, at the time when the fritting phenomenon took place. The graph ofFIG. 9 shows that the voltage and the current are increased inproportion after occurrence of the fritting phenomenon because thecurrent in the fritting time did not reach the limiting current, andthat the voltage and the current are rendered constant at the time whenthe limiting current is reached.

2. Relationship Between Needle Pressure and Fritting Voltage

The term “fritting voltage” denotes the voltage value at the time whenthe current briefly exceeded 1 mA for the first time. The probe used wasformed of W, BeCu or Pd. Each of FIGS. 10 to 12 are graphs showing therelationship between the needle pressure of the probe and the frittingvoltage. In the graphs of FIGS. 10 to 12, the probability with the totalvalue set at 1 is plotted on the ordinate. The distribution of thefritting voltage in the case of using the W probe, the BeCu probe andthe Pd probe is classified by the needle pressure. A needle pressure of0.001 g (marked by x), 0.005 g (marked by Δ), 0.02 g (marked by ∘) and0.1 g (marked by □) was applied to each probe. FIG. 10 illustrates thecase where the W probe was used, FIG. 11 illustrates the case where theBeCu probe was used, and FIG. 12 illustrates the case where the Pd probewas used.

As is apparent from FIGS. 10 to 12, the fritting voltage is distributedin two points of around 13 V and around 5 V in the case where the needlepressure is low. With an increase in the needle pressure, the peakvoltage is generally shifted toward the lower voltage and, at the sametime, a peak appears in a point not higher than 1 V. If the needlepressure is increased to 0.1 g, a peak not lower than 13 V iseliminated, and the current begins to flow even at a voltage less than 1V. Also, it appears that the peak at 5 V is shifted to the point ofabout 3 V.

The experimental data suggests the situations given below:

(1) There are two kinds of insulating film.

A voltage of about 5 V is required for breaking one of these insulatingfilms, and a voltage of about 8 V (=13 V−5 V) is required for thebreakage of the other insulating film. There are cases where the latterinsulating film is present and where the latter insulating film is notpresent.

(2) If the needle pressure is increased, the probability of the frittingphenomenon occurrence under a low voltage is increased. Under the needlepressure of 0.1 g, an insulating film exhibiting a breakdown voltage of8 V does not exist. If the needle pressure is increased, a peak appearsunder the voltage of 1 V. It is considered reasonable to understand thatthe peak appearance is not due to the insulation breakdown but due tothe mechanical breakdown.

(3) The insulating film is considered to be formed of an oxide film ofaluminum, an oxide film of a probe material or a contaminated layer ofwater, etc.

(4) It is considered reasonable to understand that, if the needlepressure is set at 0.1 g, a fritting phenomenon is brought aboutsubstantially without fail under a voltage not higher than 5 V.

3. The Relationship Between Maximum Current and Contact Resistance.

The maximum current and the contact resistance at the fritting time weremeasured by using a W probe, a BeCu probe and a Pd probe, with theresults as shown in the graphs of FIGS. 13 to 15. Specifically, FIGS. 13to 15 are graphs showing the relationship between the maximum currentand the contact resistance in the cases of using a W probe, a BeCu probeand a Pd probe, respectively. The term “maximum current” denotes themaximum value of the current flowing the instant the fritting phenomenontook place. Also, the term “contact resistance” denotes the contactresistance value when the current is set at 1 mA after the frittingphenomenon. In each graph, the mark □ denotes the result of themeasurement by the voltage controlled mode, with the mark Δ denoting theresult of the measurement by the current controlled mode.

In each probe, it is observed that the resistance is lowered with theincrease in the current. In the case of the W probe and the BeCu probe,it is seen that the resistance is lowered to 1 Ω or less if the maximumcurrent exceeding 0.5 A flows. Also, where the current is the same, theW probe and the BeCu probe exhibit substantially the same contactresistance value. On the other hand, the Pd probe exhibits a contactresistance value 1.5 times as much as the contact resistance value foreach of the W probe and the BeCu probe. This experimental data supportsthe theory that the maximum current of the fritting should be increasedin order to obtain a low contact resistance.

4. The Relationship Between the Fritting Voltage and the Maximum Current

FIG. 16 shows the relationship between the voltage (fritting voltage)and the current at the time of fritting (the instant the current notlower than 1 mA is detected). The plot in this case was on the line of25 Ω, which was coincident with the circuit resistance. FIG. 17 showsthe relationship between the fritting voltage and the maximum current.According to FIG. 17, when the current flowing in the fritting time,i.e., the current shown in FIG. 16, is smaller than the limitingcurrent, the current continues to increase after the fritting to reachthe limiting current (see FIG. 9). When the fritting voltage is high,the current, at the instant of fritting, constitutes the maximumcurrent. In this embodiment, the maximum current was 300 mA in view ofthe capacity of the power source. It is considered reasonable tounderstand that it is possible to stably obtain the contact resistancenot higher than 1 Ω as shown in FIGS. 13 to 15 in the case of using apower source capable of flowing current not lower than 500 mA.

In order to control the voltage applied to the contact portion at thetime of fritting, an experiment was conducted in which the probe wasbrought into contact with the electrode with the voltage set constant.Where a voltage of 30 V was applied, it was possible to flow the currentfar exceeding the current limiter at the instant of fritting. Theresults of the experiment, which are not shown in the drawing, werefound to conform well with the results shown in FIGS. 13 to 15,supporting the theory that the contact resistance can be lowered with anincrease in the maximum current.

5. Relationship Between Contact Resistance and Separating Force

Measured was the separating force when the probe was moved away from theelectrode, with the results as shown in FIGS. 18 to 20. FIG. 18 coversthe case of using a W probe, FIG. 19 covers the case of using a BeCuprobe, and FIG. 20 covers the case of using a Pd probe. The experimentaldata given in FIGS. 18 to 20 support that the separating force is smallwhen the contact resistance is high. It has been found that theseparating force is increased with a decrease in the contact resistance.It is considered reasonable to understand that the separating force isrelated to the area of the true contact portion. Since metals are bondedto each other in the true contact portion, it is considered reasonableto understand that the separating force between the metal members isproportional to the area and that, if the contact area is increased, thecontact resistance is decreased. Under the same contact resistance, thePd probe has the largest separating force, and the separating force isdecreased in the order of the BeCu probe and the W probe.

The present invention is not limited to each of the embodimentsdescribed above. Any apparatus having the circuit construction capableof bringing about the fritting phenomenon are included in the technicalscope of the present invention. In each of the embodiments describedabove, the needle pressure was changed within a range of 0.001 g and 0.1g. However, the present invention is not limited to the needle pressurefalling within the range noted above. It suffices for the needlepressure to be lower than the present level of the needle pressure,i.e., 10 to 20 g/probe, and to be capable of obtaining the frittingphenomenon. In short, the needle pressure is not limited to a specifiedrange in the present invention. It has been pointed out in conjunctionwith the embodiments described above that the contact resistance betweenthe probe and the electrode is lowered with the increase in the maximumcurrent at time of fritting. However, it is possible for the current, atthe time of fritting, to be low. The current is not limited to aspecified range in the present invention as far as the current iscapable of obtaining the fritting phenomenon.

According to the embodiments of the present invention, it is possible tomarkedly lower the needle pressure. According to the embodiments, it ispossible to eliminate the damage done to the inspection electrode and toprolong the life of the probe when used repeatedly. Further, accordingto the embodiments, it is possible to provide an inspection method andan inspection apparatus, which permit eliminating the necessity forapplying a cleaning treatment to the probe and which permit improvingthe inspecting efficiency.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A method of inspecting a target object to beinspected, comprising the steps of: bringing about a fritting phenomenonusing at least one probe in a part of the insulating film formed on aninspection electrode of the target object to be inspected so as to breaka part of the insulating film; bringing the at least one probe, used tobrine about the fritting phenomenon, into electrical contact with thesurface of a part of the inspection electrode, the insulating film ofthe part of the inspection electrode having been broken by the frittingphenomenon; and inspecting the electrical characteristics of the targetobject by using a tester connected to the at least one probe, whereinsaid step of breaking a part of the insulating film comprises the stepsof: bringing the at least one probe and a second probe into contact withthe inspection electrode of the target object; and applying a voltagebetween the at least one probe and the second probe so as to bring aboutthe fritting phenomenon in the insulating film formed on the surface ofthe inspection electrode, and wherein said step of inspecting theelectrical characteristics of the target object to be inspected byutilizing the at least one probe further includes electricallydisconnecting the second probe from the inspection electrode comprisesthe step of electrically by physically separating the second probe fromthe inspection electrode.
 2. The inspection method according to claim 1,wherein said physically separating step is performed by utilizing atleast one of a piezo element, a bimetal, and an electrostatic element.3. A method of inspecting a target object to be inspected, comprisingthe steps of: bringing about a fritting phenomenon using at least oneprobe in a part of the insulating film formed on an inspection electrodeof the target object to be inspected so as to break a part of theinsulating film; bringing the at least one probe, used to bring aboutthe fritting phenomenon, into electrical contact with the surface of apart of the inspection electrode, the insulating film of the part of theinspection electrode having been broken by the fritting phenomenon; andinspecting the electrical characteristics of the target object by usinga tester connected to the at least one probe, wherein said step ofbreaking a part of the insulating film comprises the steps of: bringingthe at least one probe and a second probe into contact with theinspection electrode of the target object; and applying a voltagebetween the at least one probe and the second probe so as to bring aboutthe fritting phenomenon in the insulating film formed on the surface ofthe inspection electrode, and inspecting the electrical characteristicsof the target object to be inspected by utilizing the at least one probeand while the second probe remains in contact with the surface of a partof the inspection electrode, the insulating film of the part having beenbroken by the fritting phenomenon which has been brought about withinthe insulating film; wherein said step of inspecting the electricalcharacteristics of the target object to be inspected by utilizing the atleast one probe further comprises the step of electrically disconnectingthe second probe not being used for inspecting from at least one of thetester and the inspection electrode.